The present invention relates generally to protection of intellectual property rights, and specifically to prevention of unauthorized copying of recorded, computer-readable media.
Compact disk (CD) recordings are a preferred means for distributing both digital audio recordings and computer software. CD audio recordings are almost universally made in accordance with standard 908 of the International Electrotechnical Commission (IEC), entitled xe2x80x9cCompact Disc Digital Audio Systemxe2x80x9d (Geneva, Switzerland, 1987), which is incorporated herein by reference. The 908 standard defines how audio data are to be encoded and recorded on the disk, enabling the data to be played back using standard digital decoding chips. Different standards apply to other types of data, such as computer software and video, which may be recorded on CD, as well. The various types of CDs and standards for CD recording and data storage are described, for example, in a booklet entitled xe2x80x9cThe CD Family,xe2x80x9d published by Philips Consumer Electronics B.V. (Eindhoven, Netherlands), which is incorporated herein by reference. A xe2x80x9croad mapxe2x80x9d shown on page 29 of the booklet lists different formats that exist among members of the xe2x80x9cCD family.xe2x80x9d
FIG. 1 is a block diagram illustrating the structure of a frame 20 of audio data for storage on an audio CD, in accordance with the IEC 908 standard. Each such frame comprises one control symbol 24, followed by thirty-two data symbols 28. Each symbol is spaced from the preceding one by a separator 30 comprising three auxiliary bits. A block of data on the CD comprises ninety-eight frames, each of which is separated from the preceding frame by a twenty-four-bit synchronization pattern 22.
Each symbol 28 recorded on the CD in frame 20 comprises fourteen channel bits, which correspond to a single byte of binary input data. Each of the 256 possible byte values is encoded in a process of eight-to-fourteen bit modulation (known as xe2x80x9cEFMxe2x80x9d modulation) as a fourteen-bit code, specified in the IEC 908 standard. A characteristic of the EFM codes is that over a run of coded data of a specified maximum length Tmax, including successive symbols 28 and separators 30, there will always be at least one transition (from zero to one or from one to zero). Tmax is specified by the standard to be 11 channel bits long. When the data are read out from the CD, any absence of such a transition over the course of 12 successive bits will be noted as a medium error.
Following control symbol 24, each frame 20 comprises two data segments 26 and 34 and two error correction segments 32 and 36. Each data segment comprises twelve symbols, containing data and parity information, typically corresponding to digitized audio data. Error corrections segments 32 and 36 each comprise four symbols, which are calculated based on the data in segments 26 and 34 using a Cross Interleave Reed Solomon Code (CIRC), as specified by the 908 standard. The CIRC segments are read during playback and are used to identify errors in the corresponding data segments. Dedicated, proprietary processors, typically based on custom integrated circuit chips, are used in CD players to correct the errors if possible and to conceal those errors that cannot be corrected, as described further hereinbelow.
FIG. 2 is a schematic block diagram illustrating the functions of an integrated circuit (IC) processor 40 used for digital processing of data read from a CD, as is known in the art. The functional blocks shown in FIG. 2 are typical of commercially-available ICs, such as the SAA7345 and SAA7348 devices produced by Philips Semiconductors (Eindhoven, The Netherlands), which are used in common audio CD players.
Data are read from the CD by an optical reading head (not shown) and are input to a phase locked loop (PLL) 42 for synchronization purposes. Fourteen-bit data segments 28 are converted to eight-bit symbols by an EFM demodulator 44 and are then stored by a first-in-first-out (FIFO) memory 46. An error corrector 48 compares the audio data read from data segments 26 and 34 to the corresponding CIRC data in segments 32 and 36. If an error is found, corrector 48 attempts to correct the data, using the CIRC information. Such correction is not always possible, however. Corrector 48 sets indicator flags 50 depending on whether an error was detected and whether it could be corrected.
Data from error corrector 48 is input to a digital audio processing circuit 52. If flags 50 indicate that there was an uncorrectable error in the data, an interpolator 54 conceals the erroneous value either by holding a preceding data value or by interpolating between adjacent values. The erroneous value itself is discarded. A filter 56 processes the data to enhance audio quality, and a data interface 58 formats the data for conversion to analog form by a digital/analog converter (DAC) 59. Although some processing circuits can provide a digital output of the xe2x80x9crawxe2x80x9d data, without error correction or concealment, special equipment is required to deal with this digital output, and such equipment is generally available only to established recording studios.
Original CDs are produced by stamping plastic blanks with a master mold piece, which is produced using costly, specialized equipment. Because of the high cost of CD recording equipment, CD recordings were considered, until recently, to be relatively secure against unauthorized copying. This situation has changed recently, as inexpensive CD recording devices and read/write media have become available to consumers. Thus, it is now easy, using a conventional personal computer with a read/write CD drive, or with one read drive and one write drive, to make exact, digital copies of all types of CDs. The CD content is read out by the computer, byte by byte, from one CD, typically a legitimately-purchased original CD, and then written to a blank CD so as to make a pirate copy. Similar copying methods may be used with other media, such as DVD (Digital Video Disks, also known as Digital Versatile Disks). Financial losses to the recording and software industries due to such pirate copying are estimated to be in the billions of dollars.
It is an object of the present invention to provide improved methods and apparatus for preventing unauthorized copying of recorded, computer-readable media.
It is a further object of some aspects of the present invention to provide methods and apparatus for producing compact disks that are resistant to unauthorized copying.
It is yet another object of some aspects of the present invention to provide methods and apparatus for preventing unauthorized digital copying of audio disks.
It is still a further object of some aspects of the present invention to provide methods and apparatus to preventing unauthorized copying of software disks.
In preferred embodiments of the present invention, errors are intentionally introduced into the coded content of an original digitally-recorded medium. The content of the medium further includes ancillary data, such as error detection codes or a program routine, that enable a processor in a conventional playback device, reading the original medium in accordance with a given recording standard, to automatically overcome the errors. Typically the ancillary data enable the processor either to correct or conceal the errors during playback or to ignore them altogether. When an unauthorized copy is made of the medium, however, the ancillary data are ineffective in overcoming the intentional errors in the original medium, with the result that faults occur in the copy that are substantially unrecoverable. In other words, the present invention takes advantage of error-avoidance features of the recording standard in an unexpected way, using recoverable errors introduced in the original medium to cause more serious, unrecoverable faults to be generated in the copy.
Preferred embodiments of the present invention are described hereinbelow with reference to digital compact disks (CDs) and the IEC 908 standard, which applies to audio CDs. It will be appreciated, however, that the principles of the present invention may likewise be applied to other digital recording media and standards, which like audio CDs, employ techniques of encoding and error correction that can be exploited using methods similar to those described herein. The various members of the CD family, such as CD-ROM, DVD and other formats listed in the above-mentioned xe2x80x9cCD Familyxe2x80x9d booklet, are particularly suited for application of such methods.
In some preferred embodiments of the present invention, the errors in the data are introduced after the data have been encoded in the form of a modulated data stream for driving a recording device, such as a laser beam recorder used in producing a CD master. An error generator produces a modified modulated data stream, including the intentional errors, and the modified data stream is used to drive the recording device. Such an error generator is advantageous in that it allows the present invention to be implemented in a recording facility with only minimal modification to existing infrastructure and equipment. Alternatively, the functionality of the present invention may be implemented in equipment that is used to perform other data encoding and modulation functions connected with recording on the medium, without separate, dedicated hardware for this purpose.
In some preferred embodiments of the present invention, applicable particularly to audio and video recordings, the medium contains segments of recorded data, which are interspersed with error detection codes, or error correcting codes, as are known in the art. Ordinarily, when a segment of recorded data is read out from the medium, and the corresponding code indicates that an uncorrectable error is present in the segment, the erroneous data are concealed by interpolation between neighboring data values, as described in the Background of the Invention, for example. During recording of the original medium, errors are introduced in certain data segments, without providing error detection codes capable of correcting such segments. Preferably the segments chosen for this purpose are those with respect to which it is determined that the normal error concealment mechanism on playback will not cause a noticeable effect in sound quality. Thus, the intentionally-introduced errors in the original medium are substantially concealed when the medium is played back.
When an unauthorized copy of the medium is made, the data segments are read out and recorded in the copy, including the intentionally-introduced errors. The equipment used to make the copy, which typically comprises a personal computer with an optical recording drive, computes new error detection codes to be recorded with the data segments on the copy. The new codes are based on the recorded data, including the intentionally-introduced errors. Therefore, when the copied medium is played back, the errors are not detected as such, and thus are not concealed by the playback equipment. The audio quality of the output is, as a consequence, unacceptably and irreparably compromised.
In other preferred embodiments of the present invention, applicable particularly to digital data recordings, an error is introduced into a selected data frame in the original medium, so as to render the frame unreadable by a standard playback device. Preferably, the error is introduced by creating a run of coded data that violates a convention imposed by an applicable recording standard, for example, a run of data bits in which no transition occurs over a duration greater than a maximum duration imposed by the standard (such as Tmax according to the IEC 908 standard). The original medium also includes or is otherwise associated with a program routine, which specifies to the playback device the locations of audio or other data blocks recorded in the medium. The device is able to skip over and ignore the erroneous frame, so that a user of the device is unaware of the error.
When an unauthorized copy is made of the medium, however, the equipment used to read out the data from the original medium will be unable to decode the erroneous frame and will therefore be unable to copy it. Instead, in recording the copy, the equipment will typically skip over the frame or block containing the error. Consequently, the data blocks following the skipped frame or block will be copied to the unauthorized copy in locations that are shifted relative to their locations in the original medium. When the program routine associated with the medium is run, in order to play back the unauthorized copy, the audio or other data blocks will not be found at the proper locations specified by the routine. The unauthorized copy is thus rendered unusable.
Alternatively, it may occur that instead of skipping the frame or block, the equipment will insert a frame or block with substitute data. Preferably, to deal with this eventuality, the program routine associated with the medium checks the data contained in the frame or block that is supposed to contain the error. If the substitute data are present instead of the expected data, the program routine will not allow the copy to be used.
In one of these preferred embodiments, the original medium comprises a disk containing computer software, recorded thereon in the form of computer-readable program files. In addition to the program files, the disk includes an audio track, in which an erroneous frame has been introduced as described above, preferably by creating a segment that has no transitions over a duration greater than Tmax, as specified by the IEC 908 standard. One or more of the program files include instructions such that when the corresponding programs are run on a computer, the computer attempts to read certain data recorded at specified locations in the audio track. When the original disk is used, the computer finds the proper data at the specified locations. When an unauthorized copy of the disk is used, however, the data in the audio track are shifted and cannot be found at their specified locations. The program ceases to run as a result.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for protecting data recorded on an original data storage medium against unauthorized copying, including:
receiving data encoded in accordance with an applicable recording standard;
altering a portion of the encoded data such that the altered data are identified as erroneous according to the standard; and
recording the data on the medium, the recorded data including ancillary data which are used by a processor in an intended application of the medium to operate upon the altered portion of the data such that the application runs in a manner substantially unaffected by the alteration of the data, but which ancillary data are ineffective in correcting the altered portion of the encoded data upon copying of the data, so that the alteration causes a substantially unrecoverable error in an unauthorized copy of the original medium.
Preferably, the medium includes a compact disk or, alternatively, a digital video disk.
Further preferably, the data include digital audio data, wherein the applicable recording standard includes standard 908 of the International Electrotechnical Commission. In a preferred embodiment, altering the portion of the encoded data includes introducing an error in a subcode Q channel to be recorded on the medium, preferably by specifying in a table of contents of the medium an erroneous value of the start time of a leadout of a track of the data to be recorded on the medium.
Additionally or alternatively, the data include computer program instructions.
In a preferred embodiment, the ancillary data include error detection codes, and altering the portion of the data includes changing a data value without changing a corresponding error detection code, such that the value is identified as erroneous using the corresponding code. Preferably, in accordance with the standard, the error detection code is recalculated upon copying of the data, so that the altered portion is no longer identified as erroneous.
Preferably, in the intended application using the original medium, the alteration of the portion of the data is concealed by interpolation based on the corresponding error detection code, wherein altering the data includes selecting a portion of the data for alteration so as to minimize the effect on the application of substituting an interpolated value of the data for a received value thereof.
Further preferably, changing the data value includes changing the value of a digital audio signal, such that when the ancillary data are not used to operate upon the altered portion, the quality of an audio output signal generated responsive to the data is noticeably degraded.
In another preferred embodiment, altering the portion of the data includes generating altered data for recording on the medium such that when the altered data are scanned by a reading device, the device identifies the alteration as a fault in the medium. Preferably, generating the altered data includes producing an extended run of consecutive data in which there is no transition between permitted levels of the data.
Preferably, generating the altered data includes introducing an alteration in a data block such that when the medium is copied, the data block is dropped from the copied medium, wherein introducing the alteration in the data block includes producing an alteration in a block containing information that is required by the processor in the course of running the application.
Alternatively or additionally, introducing the alteration in the data block includes producing an alteration in a first block which is followed in a sequence of blocks to be recorded on the medium by a second block containing information that is required by the processor in the course of running the application, such that when the medium is copied and the first data block is dropped, the second block is recorded on the copied medium in a location different from its location on the original medium.
Preferably, the application includes a computer software application, and wherein recording the data includes recording data including the altered portion in an audio track on the medium.
Preferably, receiving the data includes receiving a stream of modulated data configured for driving a recording device used in a process of recording the data on the medium, and recording the data includes outputting the data to the recording device following alteration of the data. Most preferably, the recording device includes a laser beam recorder used in generating a master for stamping the original medium.
There is also provided, in accordance with a preferred embodiment of the present invention, apparatus for protecting data recorded on an original data storage medium against unauthorized copying, including an error generator, which receives data encoded in accordance with an applicable recording standard and alters a portion of the encoded data prior to recording of the data on the medium such that the altered data are identified as erroneous according to the standard,
wherein the data recorded on the medium include ancillary data, which are used by a processor in an intended application of the medium to operate upon the altered portion of the data such that the application runs in a manner substantially unaffected by the alteration of the data, but which ancillary data are ineffective in correcting the altered portion of the encoded data upon copying of the data, so that the alteration causes a substantially unrecoverable error in an unauthorized copy of the original medium.
There is further provided, in accordance with a preferred embodiment of the present invention, apparatus for protecting data recorded on an original data storage medium against unauthorized copying, including an error generator, which receives a stream of modulated data in a format for driving a recording device used in a process of recording the data on the medium in accordance with an applicable recording standard, and which alters a portion of the encoded data prior to recording of the data on the medium and outputs the data including the altered portion to the recording device, modulated in the format in accordance with the standard.
Preferably, the recording device includes a laser beam recorder used in generating a master for stamping the original medium.
Further preferably, the applicable recording standard includes standard 908 of the International Electrotechnical Commission, wherein the stream of modulated data includes eight-to-fourteen bit modulated (EFM) data.
There is additionally provided, in accordance with a preferred embodiment of the present invention, data storage medium that is resistant to unauthorized copying, on which medium data encoded in accordance with an applicable recording standard are stored, a portion of which encoded data is altered such that the altered data are identified as erroneous according to the standard, the stored data including ancillary data which are used by a processor in an intended application of the medium to operate upon the altered portion of the data such that the application runs in a manner substantially unaffected by the alteration of the data, but which ancillary data are ineffective in correcting the altered portion of the encoded data upon copying of the data from the medium, so that the alteration causes a substantially unrecoverable error in an unauthorized copy of the medium.
Preferably, the medium includes a compact disk including digital audio data, in accordance with standard 908 of the International Electrotechnical Commission. Alternatively, the medium includes a digital video disk. Additionally or alternatively, the data include computer program instructions.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: